Cold starting enrichment systems of various types are well known. Typical examples of these systems are shown in U.S. Pat. No. 3,414,243, issued on Dec. 3, 1968, entitled "Carburetor Having A Cold Starting And Enrichment Mechanism," U.S. Pat. No. 3,789,702, issued on Feb. 5, 1974, entitled "Vacuum Control For Carburetor Power Enrichment Apparatus," U.S. Pat. No. 3,886,241, issued May 27, 1975, entitled "Carburetor Cold Enrichment Control," and U.S. Pat. No. 3,962,379, issued June 8, 1976, entitled "Carburetor Cold Enrichment System Having Automatic Choke Opener And Fast Idle Cam High Step Pulloff Apparatus." The '243 patent to Baczkowski, et al. describes an enrichment bypass system for the throttle plate which is responsive to engine manifold vacuum to control the bypass passage which is automatically closed by a thermally responsive element when the engine reaches operating temperature. The patents '702 to Price and '241 to Schubeck and '379 to Freismuth, et al. are all systems which are responsive to temperature and vacuum conditions on engine start-up which are closed when the engine reaches normal operating temperatures and pressures.
Hand operated enrichment devices are also well known wherein the operator manually opens a bypass line to momentarily enrich the fuel level on start-up of the engine and immediately closes the bypass port when the engine starts operating.